Capacitors are an essential electronic component in the electronic circuits. The capacitors are widely used in power supply filter circuits for smoothing electric power, signal coupling circuits, resonant circuits and the like. The electrolytic capacitors are one type of the capacitors and have in recent years come to be used in a variety of applications. However, the electrolytic capacitors have a relatively short operation lifetime, and thus the lifetime of many electronic circuits is directly linked to the lifetime of the electrolytic capacitors inside. For example, LEDs (light-emitting diodes) are a solid state light source with long lifetime of about 50 to 100 thousand hours, while the electrolytic capacitor has a lifetime of about 3 to 6 thousand hours. In other words, the operation lifetime of the LEDs is considerably influenced by the electrolytic capacitor used in the filter and driver circuit of the LEDs.
The electrolytic capacitor uses an electrolyte, an ionic conducting liquid, in its construction. The internal wet electrolytic chemical in the electrolytic capacitor can evaporate as it ages and therefore it will eventually fail. Generally, the load life of an electrolytic capacitor reflects the amount of changes to the fundamental electrical performance of an electrolytic capacitor under certain loading conditions in order to show the effect of aging in the capacitor while operating in a circuit. Because the higher temperature accelerates the evaporation of the electrolytic chemical, the temperature at which the load life is conducted typically indicates the maximum operating temperature rating for the electrolytic capacitor recommended by the manufacturers. The electrolytes used in the electrolytic capacitor evaporates, the load life of the electrolytic capacitor is thus rated in hours at a set temperature.
It is a general knowledge in the art of electronic and/or electrical engineering that the electrolytic capacitor gradually fails as it ages and accordingly its ESR (equivalent series resistance) increases. Since the ESR determines the amount of power loss when the capacitor is used in the filter circuit to smooth voltage, it should be kept as small as possible. The power loss in the electrolytic capacitor varies with the square of the ripple current flowing through it and is proportional to the ESR. The Low ESR is a key factor for high efficiencies in power supplies. As the electrolytic capacitor in the electronic circuit ages during normal use, its ESR will increase. Consequently the electrolytic capacitor can no longer provide its function as it is intended in the electronic circuit.
FIG. 1 shows a typical AC-DC step down rectification circuit using an electrolytic capacitor to smooth the DC voltage after rectification in the prior art. This circuit includes an isolation transformer T1 to lower a household AC voltage, for example 220 volts, to a lower voltage; a full wave bridge rectification circuit consisting of 4 diodes, D1, D2, D3 and D4, which converts the stepped-down AC voltage into the DC voltage; and an electrolytic capacitor Ecap1 for smoothing out the DC voltage.
FIG. 2a shows a normal DC output voltage waveform across the electrolytic capacitor Ecap1 for the step down AC-DC rectification circuit as shown in FIG. 1. FIG. 2b shows a simulated output voltage waveform with the ESR of the electrolytic capacitor Ecap1 turned infinitely large as if the capacitor is an open circuit. As shown in FIG. 2b, when the ESR increases to infinity to simulate the worst case scenario in the aging of the electrolytic capacitor Ecap1, the capacitor may fail to provide its intended function to smooth the output voltage. Since the AC-DC rectification circuit is usually used to power another electronic circuit, the failure in the electrolytic capacitor due to aging can negatively impact the functionality and performance of the electronic circuit as a whole.
Enormous amounts of time and efforts have been expended in an attempt to maximize the lifetime of the electrolytic capacitors as possible. For examples, the improvements in the lifetime of the capacitors can be known from US2005/0270723A1, CN101900269A, CN102222568A, and CN102136370A. However, these improvements merely relate to the structural modification of the capacitors per se.
Therefore, there is a need for a new method of regulating the operation of the capacitors in a circuit application, which can make a cost-effective improvement on the operation lifetime of the capacitors.